In my Cayin amp I use the Sovtek KT88 and the JJ 803 with excellent results. I find both as described in the tubestore description. I've used the Sovteks for many years and have found them very reliable. The JJ's are new to me.
If you want a fuller bass and something a bit more forward in the (upper)mid range the new production Tong Sols are quite good as well.
Can't help you on the AT's.
FWIW I think you might find the Sovtek 12ax7's clean and clear in tone but not particulariy warm. The JJ KT88 is supposed to sound good but may have QC issues. I'm not partial to any of the EH tubes, except for their 6CG7's, in general. I've tried. :-)
Hope that helps a bit.
Thanks Cayin!! I read before that Sovtek's has pretty good construction and has a very good reliability.
Tonight I installed a quad match of KT88's EH that I received at final 2009 . Turn on the Jolida and plum! One of the left channel got blowed?
I'm in Costa Rica, I don't know if some transportation issue happened.
So, I'm back with the original 65550's EH....
So, I'm waiting for a little bit more of advice to put my order @tubedepot or tubestore, the only store's that I have some reference in USA.
Before you swap power tubes on the Jolida you ought to set bias to the LOWEST and turn up accordingly.
Get a replacement KT88, they sound better than 6550Cs any day.
Also the glassy sound has everything to do with the cheap components in the amp.
Power supply: Filter caps, diodes.
Signal: Coupling caps
You need to find someone to upgrade the amp before it can really start playing music.
The transformers are world class and the amp has a lot of potential.
jaja...sorry! Thanks Newbee!! LOL!
Thanks Johnsonwu, can you confirm if the bias is Bias Settings: 50 millivolts + 5 mV ?
Before you swap power tubes on the Jolida you ought to set bias to the LOWEST and turn up accordingly.
I agree 100% but would add when I swap tubes I turn the bias to minimum - volume down to minimum and let them warm up for about 20 min. At that point I start to bias them up BUT not all the way. That's when I start playing music but not too loud for about another 10 - 20 min and look to see if the bias changed. I have found as I turn the volume up the tube starts to really work and heat up which influences bias. After a minimum of an hour but 2 hrs is better is when I make the final adjustment. Also keep an eye on the bias for several days after that. What I have seen is the tubes could take several to completely settle down. I have also found new tubes typically take 200-300 hrs to sound what there are going to sound like from that point on.
That being said I have an Octave V70SE that uses the same tubes. I have found changing the input tube (12ax7) will make the biggest difference in sound. My favorite now is not a 12ax7 but the Rca 5751 which has a slightly lower gain but sounds so right. After all the input tube is the first stage in amplification. Garbage in garbage out.
The drivers (12at7) controls the output tubes. For the normal *transconductance tubes (pretty much any *current production tube) I really like the Brimar 6060 yellow T or Amperex bugle boy ecc81's. For high transconductance you really want the Gec A2900/CV6091. They have the highest gain in the 12at7 family which will completely support high transconductance tubes.
* normal transconductance have a gain around 7000 where high transconductance tubes are over 10,000. Examples of high transconductance tubes are Shuguang Psvane - Eat kt88 diamonds - Ei Kt90 - vintage Gec/Gold lion/Gold Monarch KT88's. Note the Eat KT88 retails for $1800USD/Quad where the Shuguang Psvane is under $500USD/Quad for grade 'A' matching.
Edoll- I own a Jolida 502B. You are correct. Bias should be set to 50mV +/-5mV. Also note that biasing should be done w/all input cables to the amp disconnected (as per the JoLida manual). I prefer KT88s to 6550s. I ran the stock Sovtek 6550s but switched those out to JJ KT88s (great sound & bass but in my experience unreliable). Ran Penta Lab Shuguang KT88s. Good detail and upper frequency extension, but the tube that worked best for me was the Winged C KT88. Nice bass heft. Had previously upgraded small signal tubes to Mullard 12AT7s and Ei Elite 12AX7s. Replaced the fuse w/a HiFi Tuning fuse. Lastly, sent the amp to JoLida Annapolis, MD for the factory upgrade (a bargain at the price they charged back in 2009; hope you might be able to do the same). Nice improvement to bass extension and overall resolution without harshness. I really like this amp. The only reason I'm not running it day to day now is that it doesn't have quite the "oomph" I like to drive my Totem Forests. Now using Consonance Cyber 800SEs for that. The JoLida is my backup. Eventually, I'd like to get some higher efficiency floor standers (Tecton Lores?) and put the JoLida back in service as a 2nd system. Hope this is of some use to you.
I recently found out (from the "horses mouth" as it were) that you can use KT120s in the Jolida 502p...not sure what will happen (haven't tried it yet, as my 502P is new and not past the 12,416 hours and 8 minutes break-in period) but hey...there it is.
Thanks Xti16... that Octave V70SE...OMG! It's a treasure!! Germany power!
@Ghosthouse: I really appreciate your advice, I already read your post "Tube upgrades for Jolida 502B?" Thumbs Up!!!!
I need to tell you that your advice is very important, as a Jolida 502B owner...don't let it many time in the bench!
About the tubes, I was looking at the web info about the Winged SED reviews and each one said the same: very reliable tube with tight bass.
As a retired bass player, I really understand what means bass heft...so that is a very good direction to me.
I think maybe it will be interesting attach the Winged C with the Mullard's AT and Ax's... as this could represent around $350 at USA but certainly $600 after customs here in Costa Rica. Think that Winged C get me that money back for sure...
I'm trying all this days to do my homework, learning about tubes. And the Bias issue it is a big issue to me, I never hear about it until reading the topic at this forum.
So, sorry but I need to bother you Ghosthouse! and any other guy of course if has this knowledge and experience.
FYI... I don't have the manual, just a scan page that I found at polkaudio forum...weird certainly!
As I try to understand, this is the basic procedure to manual Bias a Jolida 502b:
1- Unplug the AC power cord from the Wall and replace the tubes / replace the AC power once got replaced the tubes, with God help and if Danica Patrick keep quiet without crashes...
2- Remove all the audio inputs (??) what for ? not necessary to know ? :)
3- Depress the AC power switch to OFF
4- Adjust the bias levels to the lowest setting = counter clockwise until cannot turn any further (v3, v4, v7, v8)
5- Make certain the left and right speakers cables are attached
6- Volume control at lowest setting
7- Turn On the Amp
8- Let the amp warm around 30 minutes ??
9- Get the multimeter set to D.C.V. / milivolt range setting
10- Get the 5 female jack terminal behind the Power Tubes / Black or Negative probe goes into the center terminal = #0
11- Red or Positive probe goes in the hole numbered according to the tube I want to bias (v3 correspond to hole #3, etc)
12- Starting the bias procedure by turn the relative screw via the small recessed pot closest, clockwise until 45-55 millivolts or .045 to .055 appear at the multimeter -It is true that is better set 45-46 to extend the tubes life ?
13- ?? What else ?
Sorry if my post is too confuse to read fellas...it will be my very first time as electrician and learning this stuff from english language, I'm not very good with both themes!
Edoll - that procedure looks good to me. The only thing I'd change is to make turning off the amp THE FIRST STEP. Then discconect AC cord, input cables, replace tubes etc. Turn bias pots and volume to lowest setting (full counter clockwise) before turning on amp. I don't know why they recommend disconnecting the input cables but I do it that way anyway. Leave only the speakers connected and allow time for the tubes to warm up. I'm not sure what effect being over or under the 50mV setting has on tube life. I did think being a little low (e.g., 48mV) was better than being above 50mV but I really don't know if that is how it works. Mostly I just try to get as close to 50mV as I can though things will drift a little. Not sure there's a significant effect so long as you are in the +/-5mV range. By the way, usually I'd get in the neighborhood of 50mV when the pots had been rotated to somewhere in the 12-2 o'clock position. Do the adjustment on each gradually. For me oit seems like there is a little lag before the change registers and settles on the mulitmeter. Also, when I got to the 4th pot, I'd go back and check the others again and make any adjustments for what little drift occurred. Even so, don't expect to get an exact, rock steady 50 mV on each tube. It's really not a difficult procedure just keep your multimeter cords and fingers away from the tubes!
Edoll, Re SED tubes, are you talking about the 6550's or the KT88's. FWIW, I find the 6550's linear and fairly uncolored. An excellent tube. The KT88 isn't nearly as linear - I find the mid/upper bass a bit on the full side and the upper mid range on the forward side, but in the right amp they can be really exciting. I'm using them in a Cayin A100T as I type. Both are rugged and reliable.
However, it appears that SED may no longer be shipping (or making?) tubes. The KT88's are very expensive when you find them, but the other SED's are still in the major retailers catalog.
Re question about bias setting. 45ma may extend life substantially but it will probably produce a cooler tone. Increasing setting to 55ma should produce a warmer tone. I've never measured the life expectancy at the two extremes, but years ago a major manufacturer, in their manual, recommended 50ma as optimum and maximum effective bias and said the tube life could be doubled by dropping the bias to 40ma. To get the tone I wanted I ended up at 45ma. I have another set of tube mono's and it was interesting to find that the manufacturer recommended 50ma per tube, but in a blog said he preferred a setting for tone which was about 40ma. It seems that the setting in the manual was more to obtain published results than it was to obtain an enjoyable tone.
Lots to consider..............
Thanks guys!!! U rocks!
Update coming soon.
Newbee, i'm consider the KT's , your conclusions are exactly as happened with my 6550 EH's vs the Sovtek Kt88's (the few hour that the KT's works before the blow they was with more bass delivery but maybe eith some "enclosure" or "inside the box" sound.
But i'm sure that after two swaps at 4 years the amp has been never biased.
Si, if I get new KT's, and with the Mullards AT's and AX's and doing the Bias procedure, hope to share you and enjoy a new sound as I never have it before.
Well, after compare your recommendations and research in another sites and forums, finally I bought new tubes at Upscale Audio tonight.
I found very good references of this store, especially very good references from Kevin Deal everywhere.
I think I'm very lucky to find with Kevin four matched SED Winged C KT88"s, and a matched pair of Mullard CV's 4024 and another Mullard's 12AX7 (this one the most popular)
I really was in love of the Mullard AT7 CV 4004, but this tube is very expensive, around $90 and this price rise to ¢195 each tube after customs here in my country...insane! That exceeds my budget and compromise have the KT's winged C...
The Jolida at this moment has never been biased, at least the last 4 years...and operate with the basics 6550 EH's and THREE!! 12AT7 EH's and just one 12AX7...
I hope that doing Bias Procedure, swap the EH's with the Winged C SED KT88's and get the new pair of 12AT7/ 12AX7 Mullards, results in a sound experience as I never have it before with the actual status.
Thanks a lot guys for your advice.
I learn a lot from each one of your posts.
How has it been going with the Jolida 502B? When I asked Doug from Doug's Tubes about KT88s in a Jolida 502 he said the Penta Labs KT88SC tubes were the ones to go with. Maybe give those a try later.